• Last Updated:
  • Jul 2nd, 2021 1:46 pm
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[OP]
Newbie
Dec 4, 2014
11 posts
3 upvotes
Toronto, ON

Tile over osb

Hey guys

So I’m planning on doing the tiles in my bathroom. I’ve done countless research on thinset and non recommended it on OSB subfloor. The builder for my house used a flooring lath on osb then thinset. Any recommendations on what thinset to use? Thanks
12 replies
Sr. Member
Jan 21, 2011
815 posts
336 upvotes
GTA
I like using Versa Bond from Home Depot.
A lot of professional trades people use Mapei.
I have only used 1/4” cement floor on top of osb, but ditra seems to be the recommended product on here.
Which ever you use, just make sure subfloor is screwed done properly every 8” or so.
Deal Addict
User avatar
Jan 2, 2012
3837 posts
2866 upvotes
KINGSTON,ON
lamin wrote: I like using Versa Bond from Home Depot.
A lot of professional trades people use Mapei.
I have only used 1/4” cement floor on top of osb, but ditra seems to be the recommended product on here.
Which ever you use, just make sure subfloor is screwed done properly every 8” or so.
You can also use a liquid waterproofing membrane such as Mapei Aqua Defence or Custom's Redgard.


This from Custom: "Wood-based panels like Oriented Strand Board (OSB) expands and contracts with changes in moisture content. Therefore, according to the 2012 TCNA Handbook, they are not recommended as a substrate material for direct bonding of ceramic or natural stone tile with cement mortars. In cases where OSB is to be used as an underlayment on interior floor installation it must be properly treated before the
installation of tile. If direct bonding of the ceramic tile to the OSB is required, a membrane must be installed on the OSB, before ceramic tile installation, that will compensate for the movement in the OSB due to changes in the moisture content. Custom® Building Products RedGard® Waterproofing and Crack Prevention Membrane applied at 30 mils wet film thickness will provide the needed protection. As a waterproofing agent Custom’s RedGard will protect the OSB from moisture in the thin set mortar and subsequent surface exposure."
Sr. Member
Jan 21, 2011
815 posts
336 upvotes
GTA
I used Redgard as well as it is recommended to use with versabond. I neglected to mention it as some members on here made it seem like a bad idea. I used it on the osb before cement board and again on top the cement board to help waterproof certain rooms.
Newbie
May 12, 2021
85 posts
46 upvotes
Hey that was me!!

What’s the op’s requirements? Substrate only? Waterproofing + tile substrate? Waterproofing + tile substrate + decoupling?

You don’t want to tile directly on top of OSB.
1) Lath + scratch coat is widely used in the GTA and it seem to hold up fine. Wait 1 day for scratch coat to dry before tiling.
2) Cement board on top of OSB is good, can tile right away.
3) Ditra on top of OSB, wait 1 day for Ditra to dry before tiling. Use Kerdi banding if you want waterproofing. Note there are multiple decoupling membranes available that essentially do the same thing as Ditra, substitute what every brand you like.

lamin wrote: I used Redgard as well as it is recommended to use with versabond. I neglected to mention it as some members on here made it seem like a bad idea. I used it on the osb before cement board and again on top the cement board to help waterproof certain rooms.
Sr. Member
User avatar
Sep 2, 2005
776 posts
394 upvotes
Toronto
if you’re going to use ditra, you go modified thinset like mapei ultraflex2. anything ansi 118.11

remember to dampen the osb before applying thinset.

and also remember to consider the thickness of everything for your transition.
Newbie
Oct 12, 2019
31 posts
5 upvotes
I just did this last year. I went with the thinnest Ditra over the OSB and followed all of the directions. Everything appears stable and I have an old house. I did find it very difficult to get the unmodified thinset to bond to the Ditra on that stage. I believe the OSB was absorbing the moisture and it was not coating the Ditra when I peeled it back (it tells you to check as you go by peeling it back). I had to redo it a couple times and it was quite a pain, but I eventually got a nice bond and it dried extremely strongly. I wonder if a sealant could be applied to the OSB first (or just wet it as zaius says), before the Ditra bonding. After a day of drying though, that Ditra is there for life. I went over it with a 9" high quality tile, after sealing all joints with the band. It was a long process and did raise the floor up a bit, but in the end it worked quite well.
Sr. Member
Jan 21, 2011
815 posts
336 upvotes
GTA
I know, didn’t want to call you out, lol.
Newbie
May 12, 2021
85 posts
46 upvotes
As long as you’re happy with it. You can name the technique after yourself!!
lamin wrote: I know, didn’t want to call you out, lol.
Sr. Member
Jan 21, 2011
815 posts
336 upvotes
GTA
I guess we should all do things one way, because there is only one way to do things. You have your technique, I have mines.

You still believe in using lath, tells me all I need to know about you and your technique, lol.
Sr. Member
Mar 10, 2004
762 posts
274 upvotes
lamin wrote:
You still believe in using lath, tells me all I need to know about you and your technique, lol.
I don t think there are many installs with lath. I have seen 1/8 in plywood substrates on 6 inch boards. No issue with install except the 80s tile is dated.
Newbie
May 12, 2021
85 posts
46 upvotes
I’ve demoed 5 tiled floors originally installed by builders in the GTA and 1 in Barrie. All floors were in good condition, grout all intact before the demo. All were lath on top of plywood so it seems to be an ok technique. It’s pretty cheap to do, lath + scratch coat then tile.

My preferred technique for reno is screw down the ply subfloor, add ply to achieve desired thickness then ditra.

I have patched a section of flooring in my own home when a wall was removed using lath + scratch coat. Still going strong even when my kids jump from the carpet to this section of tile.

My builder home is lath + scratch coat in the kitchen and baths and no issues. Floor is squeaky in some area but tile and grout is holding up.
tempperm wrote: I don t think there are many installs with lath. I have seen 1/8 in plywood substrates on 6 inch boards. No issue with install except the 80s tile is dated.

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